1. Field of Invention
This invention relates to a conductive silver coating which, when during the thermal fusing (firing) of the coating to a glass, silicon, ceramic or ceramic glass enamel substrate, provides infra-red absorption properties over an extended temperature range, thus reducing thermal stress differences from developing between the coating and aforementioned substrates, that would otherwise occur.
In particular, the present invention relates to a conductive silver coating that includes combining silver metal, lead, zinc and/or bismuth borosilicate glass frit(s), a co-ground blend of selenium and/or bismuth metal powder and lead, zinc and/or bismuth borosilicate glass frit composition or combination thereof; carbon black, black inorganic pigment, a staining compound which, when firing the coating to a glass, silicon, ceramic or ceramic glass enamel substrate, provide infra-red absorption properties over an extended temperature range, thus reducing thermal stress differences from developing between the coating and the aforementioned substrates, that would otherwise occur, especially if the firing cycle time is shortened.
2. Description of Related Art
Conventional conductive silver coatings are comprised primarily of silver metal and a glass frit. As users of such coatings push to increase product output with faster firing cycle times, insufficient sintering of the coating may occur. Additionally, insufficient sintering of the coating impedes adequate adhesion of the coating to the substrates. As a remedy to the foregoing problem, carbon black has been conventionally used to absorb infrared energy, thus offsetting the inherent reflective properties of the silver metal during firing. Additionally, lower melting glass frit compositions, having melt points below about 1100° F., were substituted for higher melting glass frits to improve the sintering and adhesion properties of the coating. However, because carbon black has a limited absorption range (it decomposes at 1094° F.), coatings exposed to firing temperatures above 1100° F. do not benefit from the use of carbon black, thus subjecting the substrate to greater thermal stresses between the substrate and the overlaying silver coating. Such conventional coatings were typically limited to a firing range of about 950° F. to about 1100° F. Induced stress is also exaggerated by the shorter cycle time and higher thermal temperatures used during the “firing” process. Hence, there is room for improvement in the art.